Emissions-control performance in a motor-vehicle engine system depends on effective atomization of the liquid fuel. When fuel entering the combustion chamber of an engine is inadequately atomized, increased hydrocarbon and/or other emissions may result. This effect may be especially evident shortly after a cold start of the engine, when the fuel and the engine are both cold. Moreover, ignition of the fuel under cold-start conditions may be unreliable when the fuel is inadequately atomized.
Achieving adequate cold-start fuel atomization may be especially difficult in a gasoline direct-injection (GDI) engine, where the air/fuel mixing interval is short, and in engines where high surface-tension, low-volatility alcohol fuels are used in place of gasoline. It is known, however, that a heated fuel may be atomized more easily than a cold fuel. Approaches for improving cold-start fuel atomization have therefore included heating the fuel as soon as a cold start is requested, e.g., when a driver of the motor vehicle turns the ignition key. The fuel may be heated via one or more resistively heated engine elements—injection impingement plates, ports, injectors, for example. Alternatively, the fuel may be heated via the combustion air.
These approaches all share a common feature: a wait-to-start interval beginning when the cold-start is requested and continuing until a liquid or solid body has reached a given temperature. By delaying ignition until after the wait-to-start interval, a disadvantageous trade-off between motor-vehicle cost and driver satisfaction may be manifest. Specifically, driver satisfaction may require a short wait-to-start interval, so that ignition occurs promptly after the cold-start request. But a short wait-to-start interval may require significant power-delivery from fuel-heating engine elements, resulting in increased motor-vehicle cost.
The inventors herein have recognized the disadvantages noted above and have provided an approach to address this paradox. In one embodiment, a method for providing heated fuel to a fuel injector of an engine is provided. The method comprises maintaining a volume of fuel above a start-ready temperature during a pre-start interval, the pre-start interval beginning after the engine is turned off, beginning automatically, and ending when the engine is restarted, the start-ready temperature greater than a lowest temperature of the engine during the pre-start interval. The method further comprises delivering some of the volume of fuel to the fuel injector when the engine is about to be restarted. Other embodiments of the present disclosure provide more particular methods and systems for providing heated fuel to an engine. According to the various approaches described herein, adequate cold-start fuel atomization may be provided without compromising driver satisfaction due to excessive pre-ignition delay, while at the same time reducing unnecessary heating of fuel during warm engine off conditions. Further, the approaches described herein may be enacted inexpensively in a wide variety of motor-vehicle configurations.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.